Treatment of photoflash lamp materials



Oct. 24, 1939.

H. W. HlGHRlTER TREATMENT OF PHOTOFLASH LAMP MATERIALS Filed Dec. 1, 1936 ATTORNEY graphs and the like.

Patented Oct. 24, 1939 TREATMENT OF PHOTOFLASH LAMP MATERIALS Harry W. Highriter, Verona, N.-J., asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 1, 1936, Serial No. 113,573

6 Claims.

My present invention pertains to photofiash lamps and particularly to the process of treating the aluminum foil employed in such lamps which upon combustion produces the well known intense momentary light for the taking of photo It has long been known in the art that aluminumioil which is heavy has a slower rate of com busti'on than does thinner foil. Consequently selection of the foil for utilization in photoflash lamps is made to maintain weightand thickness within prescribed limits. These sheets of foil are then packed by the manufacturer between adjacent sheets of paper and supplied to the lamp manufacturer. I have discovered, however, that despite the careful selection of the foil for proper weightcharacteristics, nevertheless, some of this foil exhibits a slower rate of combustion than is customary for such foil within the usual weight limits. Such is obvious from visual observations of the rate of combustion of individual sheets of foil packed adjacent to each other which clearly indicates a considerable difference in rate.

It is accordingly an object of my present invention to provide a photoflash lamp of the usual type with a plurality of sheets of combustible foil wherein the individual sheets have substantially equal rates of combustion. V

Another object of my present invention is the provision of a photofiash lamp wherein the uniformity of rate of combustion of the metallic foil is increased when comparing one lamp with an other. 7

Another object of my present invention is the provision of a method for treating metallic foil for photoflash lamps so that the individual sheets have substantially equal rates of combustion.

-A further object of my present invention is the provision of a method for treating aluminum foil for photoflash lamps so as to increase its rate of combustion to a desired value.

Still further objects of my present invention will become obvious to those skilled in the art by reference to the following description in conjunction with the accompanying drawing wherein the single figure shows 'a photoflash lamp constructed in accordance with my present invention.

The lamp shown in the figure comprises a sealed envelope 5 provided with the usual screw base 6. A reentrant stem protrudes interiorly of the; envelope and is sealed to the-neck portion 8 of the envelope. Leading-in wires 9 and i arecon nected to the screw base 6 and are sealed into the press portion of the reentrant stem in the usual manner for the purpose of carrying electrical energy to the igniter element l2. An exhaust tube l3 1 is also provided as iscustomary in the art for exhausting the envelope and admitting a desired gaseous mixture. An insulating baiile I4 is provided interiorlyof the envelope and supported by the stem thus forming an ignition chambef and preventing the hot products of combustion from falling in the vicinity of the seal.

Disposed within the envelope in the vicinity of the igniter l2 are a number of leaves or sheets l5 of suitable metal foil, such as aluminum, which are readily combustible upon the passage of an electric current through the lamp. As herelnbeforipointed out these sheets of foil are carefully selected so as to have substantially uniform weight and thickness but despite such selection there isfa considerable difference in the rate of combustion. Qualitative spectre-chemical analyses of the adjacent sheets of foil yields wide variations in: the contents of copper, calcium, magnesium, silicon, and iron, but it is not at the present known just what effect this chemical variation has on the rate of combustion. Since it is ini practical. to test individual sheets of foil for quality before manufacturing into lamps and as all lamps contain a plurality of sheets one of which, ifo'f poor quality, will adversely eiTect the rate of combustion, I find it expedient to treat all the leaves of foil at the same time.

' Accordingly, in order to increase the uniformity in the rate of combustion I treat such foil either after insertion into the envelope or while in its original packages and interleaved with paper. To this end l take the foil having suitable weight and thickness characteristics but an unduly slow rate of combustion and anneal it for a short period at a temperature of 150 to 500 C. Irrespective of the fact that some of the sheets in any lamp or package may have a suitable rate of combustion such annealing treatment affects their combustion ratevery little. In the case of initially slow burningzor combustible foil, however, the annealing treatment increases the rate of combustion so as to approach the rate of the satisfactory sheets and thus makes fora substantially uniform rate of comliustion.

The efllcacy of my treating process may be best appreciated by citing the results of tests which I made. Taking a package of foil of proper weight and thickness characteristics but showing a slow rate of combustion I divided it into threeparts with the toil remaining between-the paper inserts. One portion was in no way treated while another portion was heated for 1 hours in an oven maintained at a temperature of 225 C. The retained as constant as possible. The lamps were then burned and tested-photographically to determine the time interval between the beginning of the electrical impulse which ignites the foil and the maximum light emission of the lamp, which occurs when a majority of the foil is burning. This interval is expressed in the table below as Lag to peak, and is a function of the rate of combustion of the foil. Observations were also made of the maximum instantaneous. light emission, expressed in the table as Peak lumens which is related both to rate of combustion and to uniformity of such rate as between different foils in the lamp.

i Lag to Peak Treatment of foil peak umens Not annealed: Seconds Jtfillions Average .0272 2. 59

Maximum. 0294 4. 00

Minimum. 0257 1.75 Annealed 1% hours Average 0205, 4. 07

Maximum 0224 4. 8

Minimum. 0181 3.1 Annealed lV, hours at 250 Average. .0201 4. 23

Maximum 0209 5.1

Minimum 0191 3. 4

The annealing treatment of the foil, as hereinbefore stated, may be done either after the foil to the ignition temperature.

is inserted in the lamp or while in the original package. Moreover, any suitable heating medium may be used and atmospheres of air, inert or other gases, or vacuum may be employed.

Although the above table shows a time period of treatment of the order of one and one-half hours the time period required to anneal is inthe lamp when using temperatures of the higher range.

The mechanism by which annealing accomplishes the result of promoting uniformity of rate of combustion by increasing the combustion rate of initially slow burning foil .without affecting the rate of satisfactory foil, as indicated; in the above table. is not definitely known. One theory I have entertained involves the effect of cold working of metals to reduce thermal conductivity. It is reasonable to assume that, other factors of foil weight, uniformity of thickness, chemical com position, surrounding atmosphere, etc., being equal, the rate of combustion of a'foil will be higher the more readily the foil conducts heat from the part first ignited and heats other .parts It is well known that metals which have been severely cold worked, as is'the case in the beating of this foil, suffer a loss in electrical and thermal conductivity. Annealing of themetal restores the conductivity values to normal for the metal.

' Another possible explanation for the resulting ing i (iil a to 0. for seven days produced 'i io appreciable improvement, however, and it has not been possible to observe measurable loss in weight of a foil through annealing at 200 C.

As favoring the first mentioned theory I have measured an increase in electrical conductivity of the foil due to annealing. Since thermal and electrical conductivities of a metal rise or fallin closely parallel manner with treatment or annealing, I feel that this experiment indicates an increase in thermal conductivity of the foil as a result of annealing.

It thus becomes obvious to those skilled in the art that I have provided a photofiash lamp wherein the metallic foil is subjected to an annealing treatment. By such treatment the uniformity of rate of combustion of the foil is increased. Moreover, while any given package of foil may have satisfactory weight and thickness characteristics, it may also contain slow-burning foil. Yet subjecting the foil to my annealing treatment in no way impairs the rate of combustion of satisfactory sheets and 'at the same time increases the uniformity of rate of combustion of all sheets by increasing the rate of the initially slow-burning foil.

Although I have shown'and described one specific embodiment of my present invention, I do not desire to be limited thereto as various other modifications thereof may be made without departing from the spirit and scope of the appended claims.

What is claimed is:

1. A photofiash lamp comprising a seaied envelope provided with a gas containing oxygen, an igniter element in said envelope, and metallic foil disposed in said envelope in close proximity to said igniter element and combustible with the foil to cause all of said foil to have a. substantially uniform rate of combustion and to give a more uniform peak intensity.

2. A photofiash lamp comprising a. sealed envelope provided with a gas containing oxygen,

an igniter element in said envelope, and a plu- ,rality of sheets of foil adapted to be ignited upon electrical energy being supplied to said igniter element to,,pfo,duce a momentary intense light,

said foil having been annealed by heating to a temperature, not less than C. to increase the rate of combustion of the thicker foil to cause the rate of combustion of all the foil to be substantially uniform and to impart high thermal and electrical conductivity thereto and to increase the uniformity of peak intensity.

3. A photofiash lamp comprising a sealed envelope provided with a gas containing oxygen, an igniter element in said envelope, and metallic foil of substantially uniform weight and thicknessdisposed in said envelope in proximity to said igniter element and adapted to emit light upon combustion thereof with oxygen when electrical energy is supplied to said igniter element, said foil being preheated to a temperature not less than 150 C. to increase the rate of combustion a substantially uniform rate of combustion and to give a more uniform peak intensitg consists in annealing the foil by subjecting the same to a temperature of not less than 150 C. to increase the rate of combustion oi. the thicker sheets by increasing the thermal conductivity of such sheets and causing allthe foil to have a substantially uniform rate of combustion and a more uniformv peak intensity.

5. The method oi treating aluminum r611 sheets i'or photoflash lamps to increase the uniformity 9,177,108 oi the thicker foil to cause all oi saidfoil to have of the rate of combustion thereof which consists in'heating the toll at a temperature ranging from 150' to 500 C. for a period of time inversely related to the temperature.

6.' The method of treating metallic toil sheets 1 ior-photoflash lamps to increase the uniformity oi the rate of combustion thereof which consists in annealing the'sheets by subjecting the same while in interleaved condition to a temperature ranging from 150 to 500 C. for a period of time ranging from an hour or more to'a few minutes, depending upon the temperature. 

